Allow env variable prefix and setting namespace to be configured in settings provider

Author: jeremiahrose

docsite/source/settings.html.md

@@ -19,6 +19,10 @@ Application.register_provider(:settings, from: :dry_system) do
     require "your/types/module"
   end
 
+  configure do |config|
+    config.prefix = 'SOME_PREFIX_'
+  end
+
   settings do
     setting :database_url, constructor: Types::String.constrained(filled: true)
 
@@ -29,7 +33,7 @@ Application.register_provider(:settings, from: :dry_system) do
 end
 ```
 
-Your provider will then map `ENV` variables to a struct object giving access to your settings as their own methods, which you can use throughout your application:
+An optional prefix can be specified with the `config.prefix` setting inside a `configure` block. Your provider will then map `ENV` variables with the given prefix to a struct object giving access to your settings as their own methods, which you can use throughout your application:
 
 ```ruby
 Application[:settings].database_url # => "postgres://..."
@@ -65,3 +69,56 @@ Or as an injected dependency in your classes:
   end
 end
 ```
+
+## Multiple Settings Providers
+
+In some situations you may wish to have multiple settings providers registered to different namespaces, e.g `config.database` and `config.api`. This can be achieved using the `register_as` configuration option:
+
+```ruby
+# system/providers/database_settings.rb:
+
+require "dry/system/provider_sources"
+
+Application.register_provider(:database_settings, from: :dry_system, source: :settings) do
+  before :prepare do
+    require "your/types/module"
+  end
+
+  configure do |config|
+    config.register_as = 'config.database'
+  end
+
+  settings do
+    setting :url, constructor: Types::String.constrained(filled: true)
+  end
+end
+```
+
+```ruby
+# system/providers/api_settings.rb:
+
+require "dry/system/provider_sources"
+
+Application.register_provider(:api_settings, from: :dry_system, source: :settings) do
+  before :prepare do
+    require "your/types/module"
+  end
+
+  configure do |config|
+    config.register_as = 'config.api'
+  end
+
+  settings do
+    setting :base_url, constructor: Types::String.constrained(filled: true)
+  end
+end
+```
+
+The individual settings namespaces can then be accessed from the container seperately:
+
+```ruby
+Application.start(:database_settings)
+Application.start(:api_settings)
+Application['config.database'].url # => "postgres://..."
+Application['config.api'].base_url # => "https://..."
+```

lib/dry/system/provider_sources/settings.rb

@@ -6,13 +6,17 @@ module ProviderSources
       module Settings
         class Source < Dry::System::Provider::Source
           setting :store
+          setting :register_as, default: :settings
+          setting :prefix, default: ""
 
           def prepare
             require "dry/system/provider_sources/settings/config"
           end
 
           def start
-            register(:settings, settings.load(root: target.root, env: target.config.env))
+            register(config.register_as,
+                     settings.load(root: target.root, env: target.config.env,
+                                   prefix: config.prefix))
           end
 
           def settings(&block)

lib/dry/system/provider_sources/settings/config.rb

@@ -31,14 +31,14 @@ def setting_errors(errors)
         # @api private
         class Config
           # @api private
-          def self.load(root:, env:, loader: Loader)
+          def self.load(root:, env:, prefix: "", loader: Loader)
             loader = loader.new(root: root, env: env)
 
             new.tap do |settings_obj|
               errors = {}
 
               settings.to_a.each do |setting_name|
-                value = loader[setting_name.to_s.upcase]
+                value = loader[prefix + setting_name.to_s.upcase]
 
                 begin
                   settings_obj.config.public_send(:"#{setting_name}=", value) if value

spec/integration/settings_component_spec.rb

@@ -130,4 +130,101 @@
       end
     end
   end
+
+  context "With a custom prefix" do
+    subject(:system) do
+      Class.new(Dry::System::Container) do
+        setting :env
+
+        configure do |config|
+          config.root = SPEC_ROOT.join("fixtures").join("settings_test")
+          config.env = :test
+        end
+
+        register_provider(:settings, from: :dry_system) do
+          configure do |config|
+            config.prefix = "CUSTOM_PREFIX_"
+          end
+
+          before(:prepare) do
+            target_container.require_from_root "types"
+          end
+
+          settings do
+            setting :string_value, constructor: SettingsTest::Types::String
+          end
+        end
+      end
+    end
+
+    before do
+      ENV["CUSTOM_PREFIX_STRING_VALUE"] = "foo"
+    end
+
+    after do
+      ENV.delete("CUSTOM_PREFIX_STRING_VALUE")
+    end
+
+    it "sets up system settings component via ENV and .env" do
+      expect(settings.string_value).to eql("foo")
+    end
+  end
+
+  context "With multiple settings providers" do
+    subject(:system) do
+      Class.new(Dry::System::Container) do
+        setting :env
+
+        configure do |config|
+          config.root = SPEC_ROOT.join("fixtures").join("settings_test")
+          config.env = :test
+        end
+
+        register_provider(:settings_provider1, from: :dry_system, source: :settings) do
+          configure do |config|
+            config.register_as = "database_settings"
+          end
+
+          before(:prepare) do
+            target_container.require_from_root "types"
+          end
+
+          settings do
+            setting :example_port, constructor: SettingsTest::Types::Coercible::Integer
+          end
+        end
+
+        register_provider(:settings_provider2, from: :dry_system, source: :settings) do
+          configure do |config|
+            config.register_as = "api_settings"
+          end
+
+          before(:prepare) do
+            target_container.require_from_root "types"
+          end
+
+          settings do
+            setting :example_token, constructor: SettingsTest::Types::String
+          end
+        end
+      end
+    end
+
+    before do
+      ENV["EXAMPLE_PORT"] = "19"
+      ENV["EXAMPLE_TOKEN"] = "abc123"
+      system.start(:settings_provider1)
+      system.start(:settings_provider2)
+    end
+
+    after do
+      ENV.delete("EXAMPLE_PORT")
+      ENV.delete("EXAMPLE_TOKENT")
+    end
+
+    it "sets up system settings component via ENV and .env" do
+      expect(system["database_settings"].example_port).to eql(19)
+      expect(system["api_settings"].example_token).to eql("abc123")
+    end
+  end
 end